Our Work: Chesterfield rock roll & mattress
Date: February – March 2020
The Rothen Group were asked by Canal & River Trust to assist with erosion control along the Chesterfield Canal. Over a 130m stretch of canal bank had slipped into the canal which put the towpath at risk. The project involved:
Understanding access restrictions
Towpath remaining open during works
Clearing the slippage
Installing the rock rolls
Installing the rock mattresses
Backfilling with clay/topsoil & seed
This awkward access site could only be accessed via floating plant and commercial workboats. Our grab barge was deployed which could carry materials as well as self load & install the rock rolls/mattresses. It also acts as the site welfare & security as tools/equipment can be kept on the boat overnight away from the towpath. A hand held post driver was also used to drive posts to retain the rock rolls.
There were two aspects to the works; rock rolls & rock mattress. The rock roll works involved removing any slipped material from the toe of the bank, before installing a geotextile membrane at the base of the ‘new bank’. A rock roll was then placed in front, held in place by timber stakes, before clay was used as a backfill. This was then topped with topsoil & seeded.
For the rock mattresses, a clay ‘fillet’ was installed to create a ‘new bank’ before a rock mattress placed on top. This is where the capacity of the crane workboat came into its own as it could transport a micro digger to site as well as the clay, and then lift the micro digger onto the towpath to undertake the works. The mattress was again held in place by timber stakes. This form of bank protection can provide shelter for fish fry & invertebrates below the water & a range of insects, animals & plants above the water which is ideal for this more rural setting.